Method for producing light-guiding LED bodies in two spatially and temporally separate steps

ABSTRACT

The invention relates to a method for producing light-guiding LED bodies, in two casting and/or injection molding steps, from a material which is free-flowing before being finally solidified. First, the electronic components, consisting of at least one light-emitting chip and at least two electrical terminals connected to said chip, are coated by means of casting or injection molding, and are then recoated by means of casting or injection moulding, at least in one region, in a larger LED end mold. The present invention provides a method for the production of light-guiding LED bodies, whereby almost all light-emitting diodes produced have the same optical characteristics, and rejection caused by damage of the individual LED electronic elements is avoided.

This application is a National Stage of International Application No.PCT/DE02/04738, filed Dec. 23, 2002, which claims priority to DE 101 63116.2, filed Dec. 24, 2001.

BACKGROUND OF THE INVENTION

Such a method for producing LED bodies is known from EP 0,290,697 A1. Inthis method, the front electrode regions, the chip and the bond wire aredipped in a resin bath in a first step. In another step, the electrodesand the resin-coated, cured end are placed in a mold where theresin-coated end is coated with plastic by injection molding in order toproduce the LED body. In this method, the shape and the wall thicknessof the coating on the electronic components varies from batch to batch.Consequently, the finished LEDs have different emissive properties whendifferent materials are used in the individual coating steps on accountof the different relative indices of refraction. In addition, regardlessof the materials used, there exists the danger of damage to theelectronic components through uncontrolled melting of the first coating.

SUMMARY OF INVENTION

Method of producing light-guiding LED bodies from a material which isflowable before finally being solidified, in two casting and/orinjection molding steps, wherein the electronic components consisting ofat least one light-emitting chip and at least two electrical terminalconnected to the chip, are first coated by means of casting or injectionmolding, and then are again coated at least in regions by means ofcasting or injection molding in a larger final LED mold.

Consequently, the object of the present invention is to develop a methodfor producing light-guiding LED bodies in which nearly all lightemitting diodes produced have the same optical properties, and rejectsbecause of damage to the individual LED electronics are avoided.

This object is attained with the features of the main claim. To thisend, in a first casting and/or injection molding step, to manufacture anintermediate stage LED, a first flowable material is placed in a blankmold in which the electronic components have been inserted at least inareas. The intermediate stage LED is arranged in the final LED mold withits rear on the mold bottom or in the vicinity of the mold bottom,forming an annular channel between the inner side wall region of thefinal LED mold and the outer wall of the intermediate stage LED. In asecond casting and/or injection molding step, the first or a secondflowable material is introduced through the annular channel.

Using the method according to the invention, light emitting diodes areproduced by injection molding in two equivalent steps. In this method,the intermediate stage LED first produced already has great accuracy ofshape so that all LEDs are produced under comparable initial conditionsduring injection molding in the second process step. Consequently, allLEDs have a nearly identical luminous intensity and uniform emissivecharacteristics.

Moreover, an appropriate conformation of the intermediate stage LED andthe injection through an annular channel ensure that damage to the LEDelectronics is largely precluded.

BRIEF DESCRIPTION OF DRAWING

Further details of the invention are clear from the dependent claims andthe description below of a schematically represented example embodiment.

FIG. 1: LED body in longitudinal section;

FIG. 2: Cross-section of FIG. 1 beneath the electronic components;

FIG. 3: Intermediate stage LED in longitudinal section;

FIG. 4: Top view of the intermediate stage LED;

FIG. 5: Top view of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 5 show a large-volume LED (10) in a mold (30) whoselight-guiding body is produced by injection molding in at least twoinjection steps.

The LED (10) shown in FIG. 1 consists here of two bodies (21, 41). Thesmaller body is an intermediate stage LED (41), while the body thatsurrounds it at least in regions and is larger here, for example, isreferred to as the molded-on body (21).

As shown in FIGS. 3 and 4, the intermediate stage LED (41), which is theinner lower region of the LED (10) from FIG. 1, surrounds, at least inregions, the electrical terminals (1, 4) and completely surrounds thelight-emitting chip (6), a bond wire (2) and a reflector dish (5). Thelatter is part of the cathode (4), for example. The chip (6) sits in thereflector dish (5). The chip (6) contacts the anode (1) through the bondwire (2).

With regard to its spatial structure, the intermediate stage LED (41) ofthe example embodiment consists of three adjoining geometric shapes. Thebottom geometric shape is at least approximately a rectangular prism.Its lateral surface (42), whose subsections are oriented normal to thecenter line of the intermediate stage LED (41), is rounded off at threecorners. In place of the fourth corner, the lateral surface is embodiedas a flattened chamfer (43). The rectangular prism is delimited at thetop and bottom by parallel, flat end faces, for example. The bottom endface is the base (48). Adjoining the top end face (47) in a recessedmanner is a truncated right cone whose lateral surface (44) in the shapeof a truncated cone tapers away from the rectangular prism. Therectangular prism here has a width that is greater than the diameter ofthe bottom base surface of the molded-on truncated cone. A spherical cap(45) sits on the truncated cone. Located between the cap (45) and thelateral surface (44) in a longitudinal section through the intermediatestage LED (41) is a tangential transition, for example.

The material of the intermediate stage LED (41) is a transparent, e.g.colored, injection-moldable thermoplastic (49), for example a modifiedpolymethyl methacrylimide (PMMI).

The intermediate stage LED (41) is produced in a separate injectionmold, in a so-called blank mold (50). As a general rule, the electroniccomponents (1-6) of multiple intermediate stage LEDs (41) areinjection-molded in the same mold at the same time.

The molded-on body (21) is arranged around the intermediate stage LED(41). A parting line (61) that is no longer detectable on the finishedLED (10) is present between the two items (21, 41). The molded-on body(21) or the finished LED (10) has the shape of a paraboloid, forexample, at the focus of which is located the light emitting chip (6).As shown in FIG. 5, the end face (22) thereof opposite the chip (6),referred to as the primary emergent surface, has its respective halvesembodied as a Fresnel lens (23) and a diffusing surface (24) with ascale structure. Depending on its optical function, the primary emergentsurface (22) can have a simple geometric curvature, cf. convex orconcave forms, or any desired free-form solid shape. It can also beconstructed from a combination of individual regular geometric surfaceelements such as cones, pyramids, hemispheres, toroidal sections, or thelike.

The lateral paraboloidal outer surface of the molded-on body (21) shownin FIG. 1 is what is called a secondary emergent surface (25). It can bemade smooth or profiled and can take on almost any desired free-formshape. It can also be provided, either partially or completely, with atransparent or opaque coating. It can be galvanically metallized as anadditional reflector surface if desired. With smooth, for examplecurved, solid shapes as are shown in FIG. 1, total internal reflectioncan occur even without separate metallization.

To produce the molded-on body (21), the intermediate stage LED (41) isplaced in the split cavity injection mold, the so-called final LED mold(30). FIG. 1 only shows the split cavity final LED mold (30) in part. Apart of the cylindrical and paraboloid-shaped side wall areas (31, 32),a part of the side wall area (33) for forming a lug (26) in the shape ofpart of a rectangular prism, and part of the mold bottom (38) arevisible.

The rear (48) of the inserted intermediate stage LED (41) contacts themold bottom (38). The rear (48) may also be separated from the moldbottom (38) by a few millimeters if desired. The geometric center linesof the inside contour of the final LED mold (30) and the center line ofthe intermediate stage LED (41) are identical here.

After the final LED mold (30) has been closed, prior to injection, anannular channel (64) is discernible between the bottom cylindrical sidewall region (32) of the final LED mold (30) and the lateral surface (42)of the intermediate stage LED (41), see FIG. 1. This annular channel(64) has a cross-sectional area (65) that is shown in FIG. 2. Duringinjection molding, the low-viscosity material (29) is injected from theinjection zone (63) through this cross-sectional area (65), whichcontinues into the final LED mold (30), see the arrows in FIG. 1, whichindicate the injection zone (63) and the direction of injection. Ifnecessary, the cross-sectional area of the lug (26) is also used for theinjection process.

The incoming hot plastic (29) flows around the intermediate stage LED(41) during filling of the final LED mold (30). In this process, theliquid plastic (29) solubilizes the plastic (49) of the surface regionsof the intermediate stage LED (41) so that both plastics (29, 49)cross-link or melt together there. The injection zone (63) and injectiondirection shown ensure that the inrushing plastic (29) flows onlytangentially past the intermediate stage LED (41), without solubilizingit to the depth of the electronic components. This ensures protection ofthe electronic components (1-6). The fact that the lateral surface (44)is recessed back from the lateral surfaces (42, 43) reinforces thiseffect. The tapering of the lateral surface (44) in the flow directionadditionally prevents unwanted erosion of the intermediate stage LED(41).

After solidification, the two masses (29, 49) form a homogeneous plasticLED body that exhibits no refraction of light in the region of theformer parting line (61).

As an alternative to injection from the end face, the plastic (29) canalso be introduced into the annular channel through the lug (26) to formthe molded-on body (21). In this case, the plastic (29) is injected intothe lug (26) normal to the plane in which the electrodes (1, 4) lie; inFIGS. 1 and 3, this is the plane of the drawing. The injection point isin the region at or below the center of gravity of the lug area (27)shown here. The inflowing plastic is sufficiently slowed down by theopposite outer wall of the lug (26) that the plastic stream flowingtoward the intermediate stage LED (41) cannot produce a destructiveforce there.

To achieve high trueness of shape and precision of contour, aninjection-compression molding process can be used. It is alsoconceivable to separately manufacture the primary emergent surface (22)with its lens and/or diffusing surface, for example, and place it in theinjection mold ahead of time. The same applies to the secondary emergentsurface (25).

In another alternative, a light-guiding body that is slightly smallerthan the molded-on body (21) is placed in the mold above theintermediate-stage LED (41). In this case, this light-guiding body stillhas unfinished secondary emergent surfaces, for example, which is to saythat its present side surfaces do not contact the final LED mold (30).During injection molding, the still empty intermediate spaces betweenthe intermediate stage LED (41) and the inserted light-guiding body andbetween the light-guiding body and the final LED mold (30) are thenfilled. The injected plastic (29) melts the body located in the finalLED form (30) with high precision of form and short cooling time. Thelatter is a function of factors including the prior insertion of thelarge-volume, cold light-guiding body, which here comes into contactwith the newly injected liquid plastic only in a relatively thin edgeregion.

Here, too, an injection-compression molding step can also be added.

Of course, it is also possible with this method to produce a compositeof multiple LEDs instead of individual light emitting diodes.

LIST OF REFERENCE NUMBERS

-   1 Terminal, anode, electrode-   2 Bond wire, aluminum wire-   4 Terminal, cathode, electrode-   5 Reflector dish-   6 Chip-   10 LED-   21 Molded-on body, also light-guiding body in parts-   22 End face, primary emergent surface-   23 Fresnel lens-   24 Diffusing surface-   25 Paraboloidal surface, secondary emergent surface, reflector    surface; smooth-   26 Lug in the shape of part of a rectangular prism-   27 Side surface of (26)-   29 Material of the molded-on body, second material-   30 Final LED mold-   31 Side wall area, paraboloid-shaped-   32 Side wall area, cylindrical-   33 Side wall area for lug (26)-   38 Mold bottom-   41 Intermediate stage LED, protective body for electronics-   42 Lateral surface that is cylindrical and flat in areas, outer wall-   43 Flattening, chamfer, outer wall-   44 Truncated cone-shaped lateral surface, outer wall-   45 Spherical cap, outer wall-   47 End face, top, outer wall-   48 Base, rear, outer wall-   49 Material of intermediate stage LED, first material-   50 Blank mold, for example split cavity-   61 Parting line-   63 Injection zone-   64 Annular channel-   65 Cross-sectional area

1. Method for producing light-guiding LED bodies from a material whichis flowable before finally being solidified, in two injection moldingsteps, comprising: providing electronic components including at leastone light-emitting chip having at least two electrical terminalsconnected to the chip, coating said electrical components by a firstinjection molding step, and thereafter again coating at least a part ofsaid electrical components by a second injection molding step in a finalLED mold wherein said first injection molding step provides anintermediate stage LED having a cone shaped surface and one or morelateral surfaces, said intermediate LED providing a first flowablematerial placed in a blank mold in which the electronic components havebeen inserted at least in part into the mold, and said intermediatestage LED is arranged in the final LED mold with a rear of theintermediate stage LED on a mold bottom of the final LED mold, and anannular channel is formed between an inner side wall region of the finalLED mold and the one or more lateral surfaces of the intermediate stageLED, and in said second injection molding step, the first or a secondflowable material is introduced through said annular channel, whereinsaid cone shape causes the second flowable material to flow into saidfinal LED mold tangentially with respect to said intermediate LED. 2.Method from claim 1, wherein the first or the second flowable materialis introduced into the final LED mold through the cross-section of theannular channel on the mold-bottom side.
 3. Method from claim 1, whereinthe second flowable material corresponds to the first.
 4. Method fromclaim 1, wherein the side wall region adjoining the mold bottom of thefinal LED mold and laterally delimiting the annular channel iscylindrical in design, at least in the region of the annular channel. 5.Method from claim 1, wherein a center line of the blank mold isidentical to the center line of the final LED mold.
 6. The method ofclaim 1 wherein said one or more lateral surfaces of said intermediatestage LED is tapered and prevents unwanted erosion of said intermediatestage LED during said second injection molding step.
 7. The method ofclaim 1 wherein a homogenous plastic body is formed after said secondinjection molding step, wherein said homogenous plastic LED bodyexhibits no refraction of light in the region of a former parting linebetween said intermediate stage LED and said final LED.
 8. The method ofclaim 1 wherein said first injection molding step and said secondinjection molding step are injection-compression molding steps yieldinga final LED having high trueness of shape and precision of contour.